*{
    margin:0;
    padding:0;
}
.content{
    width:600px;
    height:400px;
    position: relative;
    margin: 0 auto;
    cursor: pointer;
    border: 1px solid #000;
}
#list{
    width:600px;
    height:400px;
    position: absolute;
}
#list img,#prev,#next,#btn-group{
    position: absolute;
}
.first{
    z-index: 1;
}
#prev,#next{
    width:40px;
    height:70px;
    background: url("../images/icon-slides.png");
    z-index: 99;
    border: none;
    outline: none;
    cursor: pointer;
    position: absolute;
    top:50%;
    transform: translateY(-50%);
}
#prev{
    background-position: -85px;
}
#prev:hover{
    background-position: 165px;
}
#next{
    right:0;
    background-position: 45px;
}
#next:hover{
    background-position: -42px;
}
#btn-group{
    z-index: 100;
    position: absolute;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
}
#btn-group span{
    display: inline-block;
    width: 20px;
    height: 20px;
    background-color:rgba(161, 159, 159, 0.123);
    border: 1px solid #fff;
    border-radius: 50%;
    cursor: pointer;
}
#btn-group .on{
    background: orangered;
}